1. Field of the Invention
The present invention relates to a device of assistance (=assistance device) for a user of a ladder. It is intended to provide a pulling force to a user who is climbing along a ladder or any other kind of climbing device of the same type. It is particularly useful in windmills, towers, chimneys or other constructions which needs maintenance by users who, most of the time, have also tools to carry up. Thanks to such an assistance device, the user feels a reduced weight while the device is providing assistance. This assistance can also be effective while the user is descending.
2. Description of the Related Art
Such devices are usually made of a traction rope which is looping between the two ends of the ladder and which is driven by a driving means such as an electric motor. The user hangs himself with a safety harness to the traction rope and he is thus pulled by the device but with a pulling force which is always less than the gravity force due to his weight.
Such devices are already known. For example, FR 2.440.906 for “Rampe mobile du type ascenseur ou descenseur á commande par traction sur I'élément formant rampe” is an assistance device which is operated according to the tension which is exerted on the traction rope as to switch on/activate or off/deactivate the assistance. PCT international application WO2009/126541 refers to a “tower climbing assist device” in which a load sensor is attached to the person on the lanyard connecting him to the traction rope. Application WO2003/071083 for “ladder climbing assistance device” in which an assistance device has a freely suspended weight-loaded wheel tightening the traction rope. Application WO2005/088063 for “Method for regulating the traction in a line of a ladder, climbing assistance device and ladder climbing assistance device” in which the activation and the deactivation of the assistance is a function of the result of detection or not of movements of the traction rope during predetermined periods of time. In this last device, displacements of the user results in movements of the traction rope which is sensed and when a movement is sensed for a certain period of time the assistance is activated to a predetermined high level of traction and while movements are sensed for a predetermined period of time, the traction remains activated at that predetermined high level of traction. On the contrary, when activated, if no movement is sensed for a predetermined period of time, the device is deactivated or the traction reduced to a low level.
All those known devices have some drawbacks. One of them is that the detection of movements or tension of the rope is not necessarily an indication to the real intention of the user to start moving along the ladder. For example he could have to bend himself or move only one or two steps to manipulate or open or close a trap door which is arranged along the ladder for security reasons. This could be the same for the recovering of his tools which could be hanging, attached to him in a tool bag or magnetically removably attached to a metallic part of the ladder while he his working along the ladder for example. If the sensing of movement of the traction rope is implemented, even for a certain period of time, the user will get the assistance even if he does not want it.
In addition, even if the real intention of the user could be known and the assistance device activated accordingly, at the beginning (or even at the end) of user activity, it is not certain that this is for climbing the whole ladder (or to really stop). As seen, a door may be found at the lower end (at some height) or the upper end (as a removable platform) of the ladder. As a consequence, giving a full assistance from the start of activation or deactivating the assistance when the user stops moving is not necessarily a good thing. It would be preferable to start assistance with a lower level of assistance before going to a higher level of assistance and, possibly, to decrease from higher assistance to a lower level of assistance before a possible deactivation.